#!/usr/bin/env node
//
const {Readable}=require('stream')
const rd=new Readable();
//拉取流
let c='a'.charCodeAt(0);
//读就会消费，是可写流进行read拉取的
rd._read=()=>{
  rd.push(String.fromCharCode(c++));
  if(c>'z'.charCodeAt(0)) rd.push(null);
};
rd.pipe(process.stdout)